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ENH: re-implement DataFrame.lookup. #40140

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#61471
#61185
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ENH: re-implement DataFrame.lookup.#40140
#61471
#61185
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stevenaelohraspco
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EnhancementNeeds DiscussionRequires discussion from core team before further actionReshapingConcat, Merge/Join, Stack/Unstack, Explode
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3.0
@erfannariman

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@erfannariman
erfannariman
opened on Mar 1, 2021

DataFrame.lookup was deprecated in #35224 in 1.2. After some feedback (#39171 ) I opened this ticket to discuss re-implentation of lookup in a performant way. As mentioned in the discussion on 35244: "but it would have to be performant and not be yet another indexing api".

This ticket can be a starting point for proposed methods, although the old implementation was actually quite performant look at given tests in the discussion of 35244:

pandas/pandas/core/frame.py

Lines 3848 to 3861 in b5958ee

if not self._is_mixed_type or n > thresh:
values = self.values
ridx = self.index.get_indexer(row_labels)
cidx = self.columns.get_indexer(col_labels)
if (ridx == -1).any():
raise KeyError("One or more row labels was not found")
if (cidx == -1).any():
raise KeyError("One or more column labels was not found")
flat_index = ridx * len(self.columns) + cidx
result = values.flat[flat_index]
else:
result = np.empty(n, dtype="O")
for i, (r, c) in enumerate(zip(row_labels, col_labels)):
result[i] = self._get_value(r, c)

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